OVARIAN FOLLICLES IN FERRETS AND FERRET-POLECAT HYBRIDS. 329 
any secretive capabilities which the follicle cells possess at this stage are utilised 
for transmitting to the ovum the material which is necessary for its growth and 
development. It cannot be doubted that the secreting power of the follicular 
epithelium is used for this purpose, but there is no evidence that it is not utilised 
also for the transmission to the exterior of the follicle of substances formed in 
the follicular cells ; indeed there are indications, long before the pro-oestrum appears, 
that this is the case. 
When a follicle becomes vesicular, on the appearance of its antrum, the follicle 
cells separate into two groups — the peripheral group, which forms the boundary wall 
of the antrum, and the cumulus group, which projects from the peripheral group into 
the antrum. One of the functions of the cells of both groups is to form the liquor 
folliculi. The function of some of the cells of the cumulus group is to transmit 
nutritive material to the ovum, for there is no other way than by and through the 
cumulus cells that the ovum can obtain the nutriment necessary for its growth 
and development. The protoplasm of the innermost cells of the cumulus blends 
with the outermost layer of the oolemma (figs. 41 and 43, PI. VII ; fig. 45, 
PI. VIII), and the nuclei of many of the cumulus cells lie in close contact with 
the oolemma until after insemination has taken place, then they all rapidly move 
away to the peripheral ends of the cells (figs. 41, 42, 43, PI. VII ; figs. 45, 47, 
PI. VIII). The peripheral cells of the general follicular epithelium exhibit the 
same peculiarities, but the positions of the cells are reversed, that is, the peri- 
pheral ends of the cells are in contact and fused with the external limiting 
membrane (figs. 58, 59, 60, PI. X), and the nuclei of many of the peripheral cells 
lie in close apposition with the external limiting membrane until the development 
of the follicle is completed (figs. 48, 49, PI. VIII ; figs. 54, 57, PI. IX). 
It is certain that the inner cells of the cumulus are transmitting material to 
the ovum, and it is not unfair to assume therefore that the cells which bear the 
same relationship to the external .limiting membrane that the innermost cumulus 
cells do to the ovum may be transmitting material to the exterior of the follicle. 
The material transmitted to the exterior of the follicles in the period shortly 
before the rupture plays a part, and probably the chief part, in the production 
of the phenomena of the pro-cestrum and the oestrus, and it is to be presumed that 
the material transmitted to the exterior of the follicle in the earlier stages of 
follicular development also has some function ; that function is, I believe, to 
facilitate the growth of the follicles themselves. The secretion produced by an 
earlier generation of follicles enables that generation to grow to a certain stage, 
but it is not sufficient, when the demand comes to carry it on to the next stage ; 
therefore the generation dies, but part of the secretion remains, and that remainder, 
together with the supply produced by itself, enables the next generation to attain 
a further stage of development ; again the supply is not sufficient for the demand 
at a certain period, and the generation dies, but the amount of secretion left is 
